GB2199385A

GB2199385A - Anti-skid apparatus for an automotive vehicle

Info

Publication number: GB2199385A
Application number: GB08729694A
Authority: GB
Inventors: Kazutaka Kuwana; Hiroshi Kuromitsu; Hiroaki Takeuchi; Nobuyasu Nakanishi; Noboru Noguchi
Original assignee: Aisin Seiki Co Ltd
Current assignee: Aisin Corp
Priority date: 1986-12-19
Filing date: 1987-12-21
Publication date: 1988-07-06
Anticipated expiration: 2007-12-21
Also published as: US4779935A; GB2199385B; JPS63154456A; GB8729694D0

Description

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1.1 2 199385) TITLE: ANTI-SKID APPARATUS FOR AN AUTOMOTIVE VEHICLE DESCRIPTION:

The invention relates to anti-skid apparatus for an automotive vehicle. The apparatus is of a kind installed between-a master cylinder and wheel brake cylinders to prevent the wheels from locking during braking. Apparatus of this kind is the subject of Patent Specifications US 4618189, GB 2172679A and GB 2175362A, for example.

Apparatus according to the invention comprises a changeover valve for positioning in a primary fluid passage between a master cylinder and a wheel brake cylinder, the changeover valve having a first operating position connecting the said cylinders and a second operating position connecting the wheel brake cylinder with a reservoir a controller for switching the changeover valve from the first operating position to the second when the wheel tends to lock on braking, a pump for pumping brake fluid from the reservoir through a check valve. to the primary fluid passage between the master cylinder and the changeover valve, and a cutoff valve in the primary fluid passage between the -master cylinder and the changeover valve for inhibiting flow when the pressure from the master cylinder exceeds that -from the wheel brake cylinder by a predetermined amount.

This arrangement can be of simple construction and adapted to prevent "kick-back" of the brake pedal due to a return of fluid from the pump to the master cylinder. Thus the cut-off valve will not be opened even if the hydraulic pressure in the master cylinder becomes higher than that in the wheel brake cylinder. A valve preferably regulates the hydraulic pressure pumped in accordance with the pressure of the wheel brake 'cylinder, and thereby eliminates an unnecessary rise of the hydraulic pressure in the pump.

DRAWINGS:

FIG. 1 is a schematic illustration of anti-skid apparatus according to the inv.ention; and FIG. 2 is a diagram showing the variation in hydraulic pressure of a master cylinder and a wheel brake cylinder in FIG. 1.

Referring to FIG. 1, a braking, system for an automotive vehicle which includes a master cylinder 11 to be activated by depression of a brake pedal 10. A hydraulic pressure developed In the master cylinder 11 is ap p-1 1 ed to a wheel brake cylinder 12 provided for a vehicle wheel 13. which is one of four wheels of the vehicle. Only the vehicle wheel 13 is illustrated in FIG. 1 In the interest of simplification. since the construction and function of other vehicle wheels are the same as those of the vehicle wheel 13.

The braking system includes an anti-skid apparatus which comprises a speed sensor 25 for detecting the rotational speed of the vehicle wheel 13 and a controller 29 for producing an electric control signal depending upon the output of the speed sensor 25. The anti-skid apparatus further comprises a cut-off valve 40 and a regulator valve 50 which are assembled within a common housing. a changeover valve 21, a reservoi.r 22, a fluid pump 23. a pump motor 27, a driving circuit 28 and a check valve 24. The master cylinder 11 is communicated with the wheel brake cylinder 12 through a primary fluid passage comprising a first passage 31. a second passage 32 and a third passage 33. The master cylinder 11 is conne cted to the cut-of f va 1v c 4 0 through the f 1 rst passage 3 1. and the cut- of f valve 40 is connected to the changeove,r v-alve 21 through the second passage 32.

The changeover valve 21 is a solenoid-operated directional control valve having three ports and taking two positions. which Is arranged to, be energized in response to' the electric control signal from the controller 29 to control the hydraulic Pressure applied to the wheel brake cylinder 12. The changeover valve 21 is connected through a reservoir Passage 35 to the reservoir 22, which is also connected to the fluid pump 23 through an inlet passage 37. The reservoir 22 has a piston 22a received in a housing communicated with the reservoir passage 35, the inlet passage 37 and a recirculation passage 36 through a port. The piston 22a is biased by a spring 22b toward the port, and movable against biasing force of the spring 22b to define a chamber whose volume is variable. The fluid pump 23 is operated by the pump motor 27 which -is actuated by the driving circuit 28 in response to the electric control signal from the controller 29. The fluid pump 23 is connected to the second passage 32 of the primary fluid passage via the check valve 24 which is disposed in a pump passage 38 and allows a fluid flow only in one direction from the fluid pump 23 toward the second passage 32. Accordingly, the brake fluid reserved in the reservoir 22 is pumped out by the f luid pump 23, and returned to the second passage 32.

The changeover valve 21 is selectively placed in one of a first operating position and a second operating position. In the first operating position, the third passage 33 is held in communication with the second passage 32, so that the wheel brake cylinder 12 is communicated with the master cylinder 11 via the cut-off valve 40, as long as the cut-off valve 40 allows the flow of the brake fluid therethrough. In this position, therefore, the hydraulic pressure in the wheel brake cylinder 12 rises with the brake f luid delivered to the second passage 32 f rom the ma'ster cylinder 11 via the cut-off valve 40 or from the fluid pump 23. In the second position, the third passage 33 is held in communication 1 4 -14 -5with the reservoir passage 35, so that the wheel brake cylinder 12 is communicated with the reservoir 22. In this position, the hydraulic pressure in the wheel brake cylinder 12 drops with'the 'brake fluid discharged from the wheel brake cylinder 12 to the reservoir 22. The changeover valve 21 is operated under the control of the controller 29 which comprises a microcomputer. The solenoid of the changeover valve 21 is, energized in response to the electric control signal from the controller 29. The controller 29 receives a braking signal transmitted by a detector switch 26 which detects a position of-the brake pedal 10, and a speed signal transmi tted by the speed sensor 25. Depending upon th-.e speed signal the controller 29 determines a degree of slip of the vehicle wheel 13 on the road surface and generates the electric control signal in the manner known in the art. The pump motor 27 is also controlled by the controller 29 through the driving circuit 28 which is actuated when an anti-skid control of the hydraulic pressure in the wheel brake cylinder 12 is started. The fluid pump 23 is held operated by the pump motor 27 as long as the anti- skid control of the hydraulic pressure continues.

The cut-off valve 40 is disposed between the first p assage 31 and the second passage 32, more specifically in a portion of the primary fluid passage between the master cylinder 11 and a point of the second passage 32 where the pump passage 38 is connected. housing 46 of the cut-off valve 40 is formed with a valve chamber 47 and a piston chamber 48 which is communicated with the valve chamber 47 through a hole which is provided in a partition wall of the housing 46 between the valve chamber 47 and -6the piston chamber 48. The valve chamber 47 is formed with a valve s e a t 4 1 a r c u n d t h a t h o 1 e. A s p h e r i c a 1 v a 1 v e m e m b.e r 4 2 i 5 accommodated in the valve chamber 47 and biased by a spring 43 toward the valve seat 41. In concentric relation with the valve chamber 47, is formed the piston chamber 48 within which a piston 44 is slidably received in a substantially fluid-tight condition with respect to the inner surface of the piston chamber 48. The piston 44 is biased by a spring 45, whose biasing force is larger than that of the spring 43, toward a shoulder portion 48c formed in the inner surface of the piston chamber 48. The piston 44 has a protrusion 44a formed at its one end facing with the valve chamber 47. The protrusion 44z extends through the hole between the valve chamber 47 and the piston chamber 48 for abutting contact with the spherical valve member 42. The length of the protrusion 44a is deterEined so that the protrusion 44a keeps the spherical valve ineiLber 42 away f rom the valve seat 41 by a slight distance when the piston 44 is located at its fully advanced position at which the protrusion 44a abuts on the spherical valve member 42. The valve chamber 47 is communicated with the master cylinder 11 through the first passage 31. The piston chamber 48 is divided by the piston 44 into two chambers, a first piston chamber 48a and a second piston chamber 48b. The first piston chamber 48a is communicated with the second passage 32 through a port 46a. The second piston chamber 48b is communicated via a port 46b with a fourth passage 34 which is connected to the wheel brake cylinder 12. Accordingly. the cut-off valve 40 is so arranged that the cut-off valve 40 is closed when the hydraulic pressure (B) in the master cylinder 11 exceeds the 1 W 1 hydraulic pressure (A) in the wheel brake cylinder 12 by at least a predetermined value ( W), as shown in FIG.2.

As shown in FIG. 1, the cut-off valve 40 is associated with the regulator valve 50 coaxially within a common housing 46. A piston 54 is s.lidably and fluid tightly received in a regulator chamber 56 defined in the housing 46, and is biased by a spring 55 toward a valve seat 53 which is formed at- the opposite side of the cut-off valve 40. The regulator chamber 56 is divided into two chambers a first regulator chamber 56a and a second regulator chamber 56b by the p1s,ton 54. The first regulator chamber 56a is communicated with the second piston chamber 48b of the cutoff valve 40, so that the first regulator chamber 56a is applied with the hydraulic pressure of the wheel brake cylinder 12. On an open end of a port- 52, there is formed the valve seat 53, through which the second regulator chamber 56b is communicated with the recirculation passage 36. This recirculation passage 36 is communicated with the reservoir 22. The second regulator chamber 56b is also communicated with the pump passage 38 through a port 51. The piston 54 is formed, at its one end, with a valve member 54a which is biased by the spring 55 toward the valve seat53, thereby normally seated on the valve seat 53. Accordingly, the second regulator chamber 56b is applied with the hydraulic pressure o f the pumped brake fluid from the fluid pump 23 through the pump passage 38.

In the normal condition of the braking system described above, the cutoff valve 40 is normally open, so that the first passage 31 is communicated with the second passage 32, and further with the third passage 33 while the changeover valve 21 maintains its first operating position as shown in FIG. I. Upon depression of the brake pedal 10 in this condition, the pressurized brake fluid is delivered from the master cylinder 11 to the wheel brake cylinder 12 through the first passage 31, the valve chamber 47 and the first piston chamber 48a of the cut-off valve 40, the second passage 32, the changeover valve 21 and the third passage 33. Since the fluid pump 23 is held off in this condition, the hydraulic pressure of the brake fluid in the first piston chamber 48a is substantially the same as that in the second piston chamber 48b of the cut-off valve 40. That is, the piston 44 holds its position as shown in FIG. 1, so that the cut-off valve 40 holds the first passage 31 and the second passage 32 in fluid communication. Accordingly, a brake force is applied to the vehicle wheel 13, whereby the vehicle speed is reduced.

When an excessive amount of slip of the vehicle wheel 13 is detected by the controller 29 based upon the speed-signal from the speed sensor 25, the changeover valve 21 is switched from its first operating position to its second operating position, whereby the third passage 33 is communicated with the reservoir passage 35, and its fluid communication with the second passage 32 is blocked while its fluid communication with the fourth passage 34 is maintained. With the changeover valve 21 switched into its second operating position, the brake fluid is discharged from the wheel brake cylinder 12 to the reservoir 22, and thus the hydraulic pressure in the wheel brake cylinder 12 is reduced. The Pump motor 27 is also actuated by the driving circuit 28 in response to the 1 J 6 Y control signal from the controller 29, so that the fluid pump 23 starts to feed the brake fluid to the second passage 32 via the check valve 24. In this initial stage in which the changeover valve 21 is switched into its second operating position and the fluid pump 23 is activated, therefore, the hydraulic pressure in the first-piston chamber 48a of the cut-off valve 40, i.e., the hydraulic pressur.e (B) in the master cylinder 11, becomes higher than such a hydraulic pressure that is higher than the hydraulic pressure (A) in the wheel brake cylinder 12 by a predetermined value ( L P) at the time (TI), as shown in FIG. 2. Consequently, the piston 44 of the cut-off valve 40 is moved toward the regulator valve 50, whereby the spherical valve member 42 is seated on the valve seat 41 by the spring 43. Thus, the cut-off valve 40 inh! bits the flow of the brake fluid therethrough. Since the second passage 32 is blocked by the changeover valve 21 in its second operating position, the pressurized brake fluid is applied in the first piston chamber 48a of the cut-off valve 40 whereby the piston 44 maintains its position.

When the fluid pump 23 is activated during depression of the brake pedal 10. the piston 54 of the regulator valve 50 is moved in accordance with the difference in pressure between the first regulator chamber 56a and the second regulator chamber 56b. When the hydraulic pressure in the second regulator chamber 56b is incr-eased to a value which is Ugher, by a predetermined val-ue. than the hydraulic prelssure in the first regulator chamber 56a, i.e., that in the wheel brake cylinder 12, the piston 54 is moved away from the valve seat 53 and permits the flow of the brake fluid -lof r om t h e f I u 1 d p u 2 p 2 3 t o t h e r e s e r v o i r 2 2 through t h e recirculation passage 36. The excessive pressurized brake fluid from the fluid pump 23 is forced into the reservoir 22 and stored therein. On the other hand, when the hydraul i c pressure in the first regulator chamber 56a is higher than that in the second regulator chamber 56b, the valve member 54a is seated on the valve seat 53. Accordingly, the hydraulic pressure of the pumped brake fluid from the fluid pump 23 is controlled at the value which is higher than the hydraulic pressure in the wheel brake cylinder 12 by a predetermined value, but lower than the hydraulic pressure in the master cylinder 11. Thus, the hydraulic pressure in the master cylinder 11 will not be applied to the wheel brake cylinder 12. In this condition, the changeover valve 21 is switched to its first operating position in response to the control signal from the controller 29, and the pumped brake fluid from the fluid pump 23, whose hydraulic pressure is slightly higher then that in the wheel brake cylinder 12, is fed into the wheel brake cylinder 12 through the pump passage 38, the check valve 24, the second passage 32, the changeover valve 21 and the third passage 33. Thus, the flow of the brake fluid from the fluid pump 23 toward the master cylinder 11 is prevented by the cut- off valve 40 in which the spherical valve member 42 is held seated on the valve seat 41 during the anti-skid control. The changeover valve 21 is controlled by the controller 29 so as to keep the hydraulic pressure in the wheel brake cylinder 12 within a suitable range in which the slip of the vehicle wheel 13 is held below a permissible limit.

When the anti-skid control is terminated and the brake 4 6 5- 14 _11pedal 10 is returned to its original position, the changeover valve 21 is returned to its normal first operating position and the f I u 1 d pump 23 is turned off by the controller 29 in response-to the signal generated from the detector switch 26. Consequently, the difference in the hydraulic pressure between the first piston chamber 48a and the second piston chamber 48b disappears, and the spherical valve me-mber 42 and the piston 44 are returned to their normal positions, as shown in FIG. 1. Then, the brake fluid in the reservoir 22 is pumped by the fluid pump 23 and returned to the master cylinder 11 via the check valve 24 and the cutoff valve 40.

It should be apparent to one skilled in the art that the above-described embodiment is merely illustrative of but a few of the many possible specific embodiments of the present invention. For example, the changeover valve 21 of three ports-two positions solenoid-operated d. irectional control valve can be substituted by a combination of an input control valve of two ports-two positions solenoid-operated directional control valve disposed between the second passage 32 and the third passage 33, and an output control valve of two ports-two positions solenoid-operated directional control valve disposed between the third passage 33 and the reservoir passage 35.

Claims

CLAIMS:

1. - Anti-skid apparatus for an automotive vehicle comprising a changeover valve for positioning in a primary fluid passage between a master cylinder and a wheel brake cylinder, the changeover valve having a first operating position connecting the said cylinders and operating position connecting the wheel brake with a reservoir, a controller for switching the changeover valve from the first operating position to the second when the wheel tends to lock on braking, a pump for pumping brake fluid from the reservoir through a check valve to the primary fluid passage between the master cylinder and the changeover valve, and a cut-off valve in the primary fluid passage between the master cylinder and the changeover valve for inhibiting flow when the pressure from the master cylinder exceeds that from the wheel brake cylinder by a predetermined amount.

a second cvlinder

2. Apparatus according to claim 1 including a recirculation passage. to the reservoir, and a regulator valve in the recirculation passage for regulating the pressure in the primary fluid passage at a value higher than that of the wheel brake cylinder by the predetermined amount.

3. Apparatus according to claim 1 wherein the cut-off valve comprises a valve member normally on a valve seat in the primary fluid passage, and a piston having at one end a hydraulic pressure from the master cylinder and at the other end hydraulic pressure from the wheel brake cylinder, the piston permitting the valve member to be moved away from the seat when the pressure from the master cylinder exceeds the pressure from the wheel brake cylinder by the predetermined amount.

4. An apparatus according to claim 2 or claim 3, wherein the regulator valve comprises a housing having at an end portion a port connected with the recirculation passage, a piston Slidable in the housing and dividing the housing into a first regulator chamber connected with the wheel brake cylinder and a second regulator chamber connected with the pump passage through the port, the piston being formed at the end facing the secondregulator chamber with a va lve member seatable on the port, and means in the first regulator chamber for biasing the piston toward the port.

5. Apparatus according to any 6receding claim wherein the cut-off valve comprises a housing having a partition wall having a hole surrounded by a valve seat and divided by the partition wall into a valve chamber connected with the master cylinder and a piston chamber connected with the changeover valve and the wheel brake cylinder, a spherical valve member in the valve chamber and seatable on the valve seat, means in the valve chamber for biasing the spherical valve member towards the valve seat, a piston slidable in the piston chamber for dividing the piston chamber into a first chamber connected with the valve chamber through the hole and also connected with-the changeover valve, and a second piston chamber connected with the wheel brake cylinder, the piston being formed with a protrusion facing the valve chamber and extending through the hole for abutting the spherical valve member, and means in the second piston chamber for biasing the piston toward the valve chamber.

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6. Apparatus according to claim 5 wherein the piston chamber is formed, around the inner surface, with a shoulder which is, smaller in inner diameter than the second piston chamber and which abuts the piston in the second piston chamber.

7. Apparatus according to claim 5 wherein the regulator valve comprises a housing having at an end portion a port connected with the recirculation passage, a piston 1 slidable in the housing and dividing the housing into a first regulator chamber connected with the wheel brake cylinder and a second regulator chamber connected with the pump passaage and the recirculation passage through the port, the piston being formed at an end facing with the second regulator chamber with a valve member seatable on the port, and means in the first regulator chamber for biasing the piston toward the port.

8. Apparatus according to claim 7 wherein the cut-off valve and the regulator valve are in a single housing, and the second piston chamber of the cut-off valve is connected with the first regulator chamber.

9. Anti-skid apparatus for an automotive vehicle substantially as herein described with reference to the drawings.

1 - PS - ii 11, AMENDED CLAIM 3. Apparatus according to claim 1 wherein the cut-off valve comprises a valve member normally spaced from a valve seat in the primary fluid passage, and a piston having at one end a hydraulic pressure from the master cylinder and at the other end hydraulic pressure from the wheel brake cylinder, the piston permitting the valve member to contact from the seat when the pressure from the master cylinder exceeds the pressure from the wheel brake cylinder by the predetermined amount.

Pubhshed 1988 at The Patent Otace, State House. 56'71 High Holborn, London WCIR 4TP. Further copies may be obtained from The Patent OMce, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd. St Mary Cray, Kent. Con. 1/87.